Fix karma upgrade

There are two problems with the karma decay upgrade that are conspiring to cluster actions around a small number of times, leading to decay happening erratically instead of smoothly:

1. The current upgrade adds each (user) modifier of a term independently, rather than as a set of inter-related actions
1. The current upgrade’s “asymptotic easing” distributor is broken in at least 2 ways.

This PR attempts to address both:
1. User actions are added round-robin, then anonymous actions are added afterward, so that they are reaped first.
1. The default distributor is replaced with a simple, linear distributor.

It is possible that there is something else that caused #13, however, I am fairly confident that these two contributed to the sudden disappearance of a bunch of karma as clumped actions were reaped.